.

t_syspread_go.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"os"
 	"runtime/pprof"
+	"syscall"
 	"time"
 )
 
@@ -13,8 +14,8 @@ import (
 const Niter = 1000000
 
 // xpread is pread(2) but aborts on an error or when fewer bytes was read
-func xpread(f *os.File, buf []byte, offset int64) {
-	n, err := f.ReadAt(buf, offset)
+func xpread(fd int, buf []byte, offset int64) {
+	n, err := syscall.Pread(fd, buf, offset)
 	if err != nil {
 		panic(err)
 	}
@@ -23,6 +24,18 @@ func xpread(f *os.File, buf []byte, offset int64) {
 	}
 }
 
+// xreadat is ReadAt but aborts on an error or when fewer bytes was read
+func xreadat(f *os.File, buf []byte, offset int64) {
+	n, err := f.ReadAt(buf, offset)
+	if err != nil {
+		panic(err)
+	}
+	if n != len(buf) {
+		panic(fmt.Errorf("readat(%v) -> %v", len(buf), n))
+	}
+}
+
+
 const BufSize = 4096
 var buf [BufSize]byte
 
@@ -50,17 +63,18 @@ func main() {
 	if err != nil {
 		log.Fatal(err)
 	}
+	fd := int(f.Fd())
 
 	for size := 0; size <= BufSize; {
 		sbuf := buf[:size]
 
 		// warmup
-		xpread(f, sbuf, /*offset=*/0)
+		xpread(fd, sbuf, /*offset=*/0)
 
 		Tstart := time.Now()
 
 		for i := 0; i < Niter; i++ {
-			xpread(f, sbuf, /*offset=*/0)
+			xpread(fd, sbuf, /*offset=*/0)
 		}
 
 		Tend := time.Now()